A robot cleaner, a sort of a mobile robot, sucks dust or debris while traveling by itself in a space such as in a house or in an office. The robot cleaner includes a sensor that senses an obstacle. The sensor, however, cannot discriminate the size or height of an obstacle in front of it. Thus, even when an obstacle that the robot cleaner can sufficiently pass over is sensed, the robot cleaner makes a detour to avoid the obstacle during its traveling.